1. Field of the Invention
The present invention relates generally to personal audio devices that include adaptive noise cancellation (ANC) and multiple drivers for differing frequency bands.
2. Background of the Invention
Wireless telephones, such as mobile/cellular telephones, cordless telephones, and other consumer audio devices, such as MP3 players, are in widespread use. Performance of such devices with respect to intelligibility can be improved by providing ANC using a reference microphone to measure ambient acoustic events and then using signal processing to insert an anti-noise signal into the output of the device to cancel the ambient acoustic events.
While most audio systems implemented for personal audio devices rely on a single output transducer, in the case of transducers mounted on the housing of a wireless telephone, or a pair of transducers when earspeakers are used or when a wireless telephone or other device employs stereo speakers, for high quality audio reproduction, it may be desirable to provide separate transducers for high and low frequencies, as in high quality earspeakers. However, when implementing ANC in such systems, the latency introduced by the crossover that splits the signals between the low frequency transducer and the high frequency transducer introduces delay, which reduces the effectiveness of the ANC system, due to the increased latency of operation.
Therefore, it would be desirable to provide a personal audio device, including a wireless telephone and/or earspeakers that provide low-latency ANC operation while using multiple output transducers that handle different frequency bands.